What are spark plugs? Why do spark plugs break windows?

Why do spark plugs break windows? Car windows are made to be reliable and withstand damage during an accident. However, if you ever get stuck inside the car and your doors are jammed, you can use a spark plug to break the windows in an emergency. You would ask why a spark plug works better at breaking a window than a hammer or any other object.

Spark plugs instantly break windows when thrown at the glass with sufficient force because they are generally made of aluminum oxide ceramic or porcelain, which concentrates a tremendous amount of energy at a single focal point on the glass.

What Are Spark Plugs?

Most things might fail at efficiently breaking window glass, but not spark plugs! As the name suggests, Spark plugs are small components that create a spark to ignite the gasoline in the internal combustion engine. The spark plug is connected to the ignition system and a central electrode through a threaded metal shell that protrudes into the cylinder.

Why do spark plugs break windows

The spark plug must be made of a hard material that can withstand high temperatures and pressure to work efficiently. Incidentally, this also makes them a perfect tool for shattering windows.

Why Do Spark Plugs Break Windows?

The insulator of a spark plug is made from aluminum oxide ceramic. It is an extremely hard material and sharp fragments of the smashed ceramic, which can break tempered glass even when thrown with a little force. Spark plugs are also called ‘ninja rocks‘ due to their ease of shattering windows.

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Almost all windows on a vehicle except for the windshield are made from tempered glass. While it is known to be strong, it is designed to shatter into small pieces for cutting down risks of injuries from a larger piece of broken glass. This is made possible by the way tempered glass is processed and manufactured.

Types Of Spark Plugs

There are three different kinds of spark plugs. Let’s take a closer look at each one of them.

Copper Spark Plug

Copper spark plugs are the market’s most common spark plug—a spark plug with a nickel alloy shell and a copper core. Copper is ideal for spark plugs due to its electrical and thermal conductivity. The only drawback is that copper is a soft metal, making the spark plugs wear out much faster.

Platinum Spark Plug

Platinum spark plugs have a platinum-coated electrode. Platinum is more rigid than copper, which makes it last longer. It has two varieties:

  • Single platinum spark plug – It has a platinum-coated electrode on the center electrode. The side electrode is made of copper. This ensures good electrical conductivity while still providing the benefits of platinum.
  • Double platinum spark plug – It has a platinum-coated electrode on both the center and side electrodes, which helps improve the spark plug’s lifespan.

Iridium Spark Plug

The iridium spark plugs are ideal for high-performance engines. It features a thin wire center electrode that fires more sparks. The electrode is coated with iridium in an Iridium spark plug which is harder than platinum making it sturdier and long-lasting.

Factors That Make A Spark Plug Shatter Windows Easily

Let’s take a look at the physics behind why spark plugs are so effective at shattering your car’s glass windows:

Why do spark plugs break windows

The Ceramic Insulator

Spark plugs are made of aluminum oxide ceramic or porcelain that focuses a lot of energy at a singular point when thrown at the glass, causing the glass to shatter.

The Weight

The ceramic material is very dense, making it heavier than most other objects of the same size. This means it also puts more pressure per square inch on the glass when you’re trying to break it.

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Steps To Use A Spark Plug To Break Your Car Window

If you ever find someone stuck in a car and need to break the windows or the windshield to get them out, here is what to do:

  • Find the spark plug in the car. The spark plugs are located at the top of the cylinder head. The piston moves down the cylinder, where it takes in a combination of air and fuel. Next, the piston travels back up to the spark plug, compressing the mixture. If there is a spare spark plug, that will work best. Don’t use a new spark plug.
  • Break the plug and remove the AC/DC converter. After tapping the spark plugs open, you can break the insulation into small chunks.
  • Throw a piece at the window. Throw the broken insulation piece at the window, and if you apply enough force and have luck on your side, the window will shatter.

How Tempered Glass Produced?

After the molten glass is shaped, it is cooled down to its solid state before further processing. Tempered glass is cooled very quickly from liquid to solid state. This allows the glass to have a lower density and a higher volume than other glass products cooled normally.

It also creates compression on the outer side and tension on the inside of the glass. In summary, tempered glass is hard and strong but has a huge amount of internal energy created by the compression and tension of the glass, which is caused during the tempering process.

Why Would Someone Want to Break a Car Window with a Spark Plug

Now that we have covered how spark plugs can break tempered glass windows, it comes to the reason why you might need to do it. Although a car window can also be broken with other tools such as a metal rod or a large stone, what would you do if you were stuck inside the car without these items?

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Why do spark plugs break windows

A spark plug is just more accessible as it can be stored anywhere and can also be found at your nearest hardware store! Moreover, it is also very easy to break a car window by using a spark plug. If you are interested in knowing how to do it, continue reading to the next section.

How to Break a Car Window with a Spark Plug?

Before getting started, it should be noted that the entire spark plug is not required for this process. We just need the porcelain fragments of the spark plug’s insulator. You will need:

  • A new or used spark plug
  • (Optional) Hammer or any similar tool for shattering the spark plug’s insulator
  • (Optional) Protective equipment to prevent injury from tiny ceramic shards

Once you have everything ready, follow these steps to break a car window

  • The first step is to shatter the spark plug’s insulator (the white part). If a hammer is available, you can smash it while holding the plug’s metal end, or you could smash it into a concrete floor, a brick wall, etc.
  • Please pick up the pieces but be careful as they are very sharp. Use protective equipment if possible.
  • Aim at the center or corners of the car window, and toss the piece(s).

If done right, the sharp edges of the porcelain fragments should create cracks in the tempered glass, and it will shatter almost instantaneously.


What is the weakest part of a car window?

A car window’s surface is weak near its edges and its center.

Do ceramic spark plugs break glass?

Yes, the ceramic insulator of a spark plug can be used for breaking glass. When thrown with a decent speed, it fractures the glass by concentrating the impact into small areas, which releases the glass’s internal energy and causes it to shatter.

What causes a broken spark plug insulator?

When an engine is knocking or misfiring, its pistons and valves overheat. It causes the electrode of a spark plug to enlarge, which in turn breaks the ceramic insulation.

Can a broken spark plug damage the engine?

Yes, and it is highly discouraged to drive a car with broken fragments from a spark plug inside as it may lead to serious damage or cause engine failure.

What liquid can break glass?

It is possible to break the glass by pouring hot water on it and immediately pouring chilled water. Due to a thermal shock, the glass will start to crack and break.

Above is information about What are spark llugs? that we have compiled. Hopefully, through the above content, you have a more detailed understanding of Why do spark plugs break windows? Thank you for reading our post.

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